The present invention is directed to a shoaling water energy conversion device and, more particularly, to a shoaling water energy conversion device for use in oceans, lakes, rivers, and other bodies of water.
The general idea of harnessing the power of waves in an ocean or a lake, or the current of a river, to produce energy has been around for many centuries. Water wheels were used to irrigate farmland and to process the crops grown thereon since antiquity. The various devices developed met with differing levels of success, but, until recently, the devices were generally used as a direct source of power. That is, the devices usually converted the power of the waves or current directly into mechanical energy, such as, for example, turning a mill for processing grain. More recent devices, those from the last century or two, have shifted to the production of electrical energy, rather than mechanical energy, which can be used to indirectly power devices located off-site. Since these recent devices convert the kinetic energy of the waves or current into electrical energy, these devices are generally known as water energy conversion devices.
The purpose of a water energy conversion device is to harvest the energy in moving water or waves. Since wave energy and energy from flowing water are renewable resources, the environmental impact is limited to the resources used for the production, installation, and dismantling of the device itself.
A great number of energy conversion systems have been proposed. Traditionally, water energy conversion devices have been classified by their placement (on shore, near shore, or off shore/deep water), rather than by the principle of operation of the device or how much energy the device can effectively produce. A conventional water energy conversion device may be placed in a great number of locations, but has been most widely used in oceans and inland riverways that are subject to greater, and more consistent, wave action or current. A conventional wave energy conversion system may be located near shore, on land near the coast, or away from the shore in deeper water and may be of a floating or submerged type. More recently, such devices have begun to be classified by their general method of producing power.
The first category of energy conversion systems includes “moving” systems, where the moving water or wave is used to move a body to produce energy. The body may in the form of an oscillating water column, a float, a roller, connected floats, a flexible body (such as a hinged plate), a fixed body (such as an airbag), and may other forms.
Most water energy conversion devices of the “moving” type are of an “up and down” type, most of which use a float. In these devices the “up and down” movement of the float as a wave passes the device is used to create a pushing/pulling force in relation to a fixed point. This fixed point can be an anchor, dampening plate, or other support apparatus. These devices use only the potential energy of the wave (i.e. the height difference between the crest and the trough of the wave) and the energy produced can never be greater than the potential energy component of the wave. The floats of these devices also often have size limitations that are dependent upon the size of the waves, since the “rolling” of the float in the wave or the riding of the float over the troughs of the waves (i.e. stretching between two wave crests) reduces the efficiency of the device. Examples of these “up and down” type devices include: the McCabe Wave Pump, which consists of three rectangular pontoons that move relative to each other as waves pass by, thereby producing energy through the movement of the pontoons; the Danish Wave Power float-pump device which uses a float that is attached to a seabed-mounted piston pump to produce energy; U.S. Pat. No. 2,093,351 to David, which discloses a float that generates electrical power through the vertical movement of the float due to wave action and the weight of the float; and U.S. Pat. No. 4,232,230 to Ames, which discloses that use of floats to activate electrical generating units supported by a base plate as the device is “rocked” by waves; and U.S. Pat. No. 4,672,222 to Ames, which discloses an apparatus with floats that utilize the vertical motion of waves to activate electrical generators located on a base or damper plate.
“Moving” type water energy conversion device may also utilize an oscillating water column to produce energy. In these devices, water, air or fluid oscillates up and down in a fixed pipe. The pressure variation of the water surface underneath the pipe forces the air above the surface of the water in the pipe to oscillate. This oscillating airflow, in turn, may be passed through a turbine and be used to produce energy. The length of the pipe is subject to size limitations, as the efficiency of the device drops if the pipe is too large relative to the size of the waves. Examples of these oscillating water colunm type devices include: the OSPREY (Ocean Swell Powered Renewable Energy) buoy, which produces energy using an oscillating water column; and the TAPCHAN (tapered channel system), which includes a gradually narrowing channel with high walls and wave deflectors that capture waves to compress air, which then drives an axial flow Wells turbine; and U.S. Pat. No. 6,360,534 to Denniss and U.S. Pat. No. 6,622,483 to Denniss, which disclose an apparatus that uses an oscillating wave surface to produce an oscillating air column that drives a turbine located at the outlet of the air chamber.
“Moving” type energy conversion systems may also utilize a roller, which can extract both kinetic and potential energy from the waves. The limitations on the energy extraction of these devices are largely dependent upon the necessity of matching the design of the device to the type and size of the waves that will be encountered. Although these devices can all extract energy from the waves, they rely on oscillating with exactly the optimal phase and amplitude in relation to the incoming waves. As such, these devices are less effective in areas where the wavelength and size of waves is variable. Most of the energy lost during the operation of roller type devices is due to friction between the water and the surface of the device.
The final type of “moving” type energy conversion systems is an impact-type device. These devices are generally constructed to use a very specific type and size of wave. Most of these devices use some type of airbag which is compressed by the impact of a wave and then allowed to return to its original position between wave fronts. Generally, when the airbag is compressed, it forces air through a turbine due to a difference in pressure, which then equalizes as the wave passes, causing the airbag to return to its original position. This oscillation of the air through the turbine produces energy. These devices may extract both kinetic and potential energy from the waves, but energy is often lost due to the uneven pulsating character of the energy delivery, regardless of whether a firm or flexible body is used. Examples of these impact type devices include: U.S. Pat. No. 4,384,456 to Boros, which describes an apparatus that serves as a breakwater and produces electrical energy through the movement of baffles through wave action; U.S. Pat. No. 4,448,020 to Wood, which discloses an apparatus that converts wave energy to electrical power by directing the flow of air or hydraulic fluid displaced by the cyclic application of wave force through a generator; and U.S. Pat. No. 4,552,514 to Hagen, which shows an apparatus that produces power when wave action causes a float to compress air, gas, or liquid in a piston and wherein the air, gas, or liquid is forced to flow through a generator.
A second category of wave energy conversion systems includes “shoaling” type systems, where the movement of the water or waves causes water to be flushed into the device. Most shoaling type energy conversion systems use ramps or slanted plates to elevate flowing or moving water to allow it to fall into or through hydro-turbines to produce energy. The limitations of these devices often depend upon the particular design. A “wash up” device converts some of the kinetic energy or the wave to potential energy by making the wave shoal over and run up an inclined plate and into a reservoir. As the water flows out of, or into, the reservoir it may be run through a turbine to produce energy. A “flush in” device makes the waves flush into the device, causing a turbine to turn and produce power. Both “wash up” and “flush in” devices will lose energy due to friction as the waves shoal up into and over the device. Examples of these “breaking” type devices include a floating wave power vessel, which consists of a steel platform having a sloping ramp that directs incoming waves into a raised basin, which then drains through a hydro-turbine generator to product energy; U.S. Pat. No. 5,443,361 to Skaarup, which shows a method of elevating flowing water or waves via a ramp wherein the elevated water is directed into an energy conversion engine; and the WavePlane made by WavePlane Production A/S, which elevates flowing water or waves via a ramp wherein the elevated water is directed into an energy conversion engine.
Other examples of conventional wave energy conversion systems having various designs may be found in other United States patents. U.S. Pat. No. 4,363,564 to Borgen describes a method and apparatus for directing energy from waves or flowing water into and through a generator to produce electrical power. U.S. Pat. No. 4,756,267 to Carr discloses a tubular mooring line with reinforced elastomeric material that may be combined with a turbine to form an electric power system. U.S. Pat. No. 6,527,504 to Skaarup describes a device that converts wave action into a whirling motion in water which is utilized to turn a turbine. U.S. Pat. No. 6,885,114 to Baarman describes a hydro-turbine unit confined within a housing wherein the plurality of paddles turn to produce electrical power in response to fluid that his force through a nozzle and directed at the paddles.
In general, wave energy conversion systems that are located offshore in deep water have the advantage of having larger waves from which to produce energy, with the disadvantage of requiring longer and more expensive underwater cables to transmit the energy to shore and more difficultly in performing maintenance on the system. On the other hand, onshore or near-shore units have the advantage of easier maintenance and installation, a shorter length of underwater cable needed to transmit the energy to shore, and not requiring deep-water moorings, but have the disadvantages of having smaller waves from which to product energy and, in some cases, meeting resistance from nearby residents due to its aesthetic effects on the shoreline.
While conventional wave energy conversion systems have been successfully developed and utilized, they are not without problems. In particular, conventional wave energy conversion systems often operate at a lower efficiency than may be desirable due to the energy loss from the wave caused by the wave's interaction with the device itself (for example, the loss of energy through the shoaling of the wave on the device and the back-pressure effect which occurs when the water is unable to properly be “cleared-out” from the exit of the device). Likewise, conventional shoaling water energy conversion devices have been limited to one method or type of energy conversion, thereby reducing the amount of energy produced by the systems.
The present invention addresses the some of the problems of these conventional wave energy conversion systems and provides an inexpensive energy conversion system that is able to operate at greater efficiency. More particularly, the present invention directs the flow of water into a hydro-turbine or pump which is uniquely efficient due to a “water foil” or “splash-away” plate located under the device which allows the free expulsion or exit of water from the exhaust of the turbine or pump. Additionally, the present invention allows the weight of the wave, from its crest to near its trough, and the kinetic energy of the lateral movement of the wave to be captured without the energy loss associated with lifting the wave. The present invention also includes forward collection plates or boards and may include a wave leveler or modifier that flattens the wave and directs the flow of the wave water into the unit, thereby increasing the fluid velocity through the device while, at the same time, adding lift to the portion of the device facing the incoming wave.